Somatic gene transfer to the pulmonary circulation may be useful in treating pulmonary hypertension, adult respiratory distress syndrome or metastatic disease to the lung. Current generation adenoviral vectors may be useful for such purposes but their gene transfer efficiency is modest after i.v. administration and concerns remain regarding immune and inflammatory responses to these constructs limiting their potential use in repetitive dosage regimens. Accordingly, non-viral vectors represent a rational alternative. The applicants have recently reported the design of a cationic lipid/protamine/DNA complex (LPD) that had physiochemical properties considerably different from cationic lipid/DNA complexes and whose behavior was more similar to a synthetic virus-like particles. LPD has a core of protamine-condensed DNA coated with a lipidic shell with a size of 50-100 nm. It is remarkably efficient in transferring reporter genes to the pulmonary circulation of intact mice but is associated with an inflammatory response that may contribute to transient gene expression and refractoriness to repeated injections at frequent intervals. To elucidate the mechanism of LPD-induced toxicity, the applicants have shown in preliminary studies that i.v. administration of LPD induces a high level of proinflammatory cytokine production which not only cause toxicity to experimental animals but also inhibit transgene expression. They have further shown that unmethylated CpG sequences in the plasmid DNA play and important role in the induction of cytokines. Intravenous administration of short, linear DNA fragments formulated in LPD leads to efficient lung transfection but is associated with significantly lower levels of cytokine production. The applicants will follow up these important findings by focusing our efforts in the following three aims. Aim 1, to further determine the molecular mechanism by which plasmid DNA contributes to LPD-induced inflammatory response and reduced transgene expression. A strategy of using short, synthetic genes to reduce toxicity will also be investigated. Aim 2, to further define the pathophysiologic response of pulmonary circulation that modifies LPD-mediated somatic gene transfer. Aim 3, to engineer LPD complexes with targeting ligands to pulmonary endothelium to improve the efficiency of gene (plasmid DNA or synthetic genes) delivery to pulmonary endothelium while maintaining the non-specific interactions with immune cells. These studies will promise to improve the efficiency of gene transfer by LPD and reduce the untoward toxicity.